Field of the Invention
The present invention relates to a wireless device, a sensor unit, a wireless unit, and a method for setting the wireless device.
Priority is claimed on Japanese Patent Application No. 2012-238749, filed Oct. 30, 2012, and Japanese Patent Application No. 2013-168897, filed Aug. 15, 2013, the contents of which are incorporated herein by reference.
Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
Conventionally, to achieve a high degree of automation at a plant, a factory, and the like, a distributed control system (DCS), in which on-site devices known as field devices (measuring devices and manipulating devices) and a control device for controlling these field devices are connected via a communications means, is constructed. While the field devices constituting such a distributed control system have hitherto mostly been ones that perform wired communication, in recent years field devices that perform wireless communication (wireless field devices) based on industrial wireless communication standards such as ISA100.11a and WirelessHART (Registered Trademark) are also being implemented.
In the wireless field device mentioned above, a sensor unit for measuring and manipulating a state quantity in the industrial process (e.g. pressure, temperature, flow rate, etc.), a wireless communication unit for performing wireless communication based on the industrial wireless communication standard, and a controller for collectively controlling the operations of the wireless field device, are assembled in a casing, and are operated by power supplied from a single power source. Since the wireless field devices need not be connected to a communication line or a communication path, and are basically installed independently at a plant or the like, most of them use an internal battery as their single power source.
In such a wireless field device, a power-saving operation is carried out to reduce battery consumption as much as possible. Specifically, when the wireless field device does not need to perform wireless communication, it is in a non-operational state (at least, a state where, to reduce power consumption, it does not send or receive wireless signals), and, only when a need to perform a wireless communication arises, it shifts to an operational state (a state that enables transmission and reception of wireless signals) and performs an operation of sending or receiving the wireless signal. Yamamoto Shūji et al., ‘World's First ISA100.11a standard Wireless Field Device’, Yokogawa Technical Report, Vol. 53, No. 2, 2010 discloses such a conventional wireless field device, wherein an input/output unit (sensor) and a wireless communication unit are provided in single structure.
As described above, in conventional wireless field devices, the sensor unit for measuring and manipulating a state quantity in the industrial process, the wireless communication unit for performing wireless communication, and the like, are assembled inside a casing and operated by power supplied from a single power source (a battery). Hence the conventional wireless field device has the following problems (1) to (3).
(1) Device Certification is Required for Each Type of Wireless Field Device
Wireless devices that perform wireless communication, and not only wireless field devices, must generally obtain certification that they conform to the laws of their respective nations (wireless standard certification). Since this wireless standard certification must basically be obtained for each type of wireless device, wireless field devices having, for example, the same type of wireless communication unit and yet having input/output units (including sensors and actuators) of different types or shapes must each obtain wireless standard certification.
In addition to the wireless standard certification mentioned above, wireless devices used in an environment where flammable gas is being used, such as wireless field devices installed at a plant, must also obtain certification that they confirm to explosion-prevention standards (explosion-prevention certification). This explosion-prevention certification requires a more complex procedure than the wireless standard certification mentioned above, and a long time is required to obtain it. Since the wireless standard certification and the explosion-prevention certification must be obtained separately in each country and region, for makers and vendors of wireless field devices and the like who attempt to expand their business on a world scale, there is a problem that enormous time, cost, and manpower are needed.
(2) Going Offline when Battery is Replaced
As described above, a wireless field device is operated by power supplied from an internal battery. In most wireless field devices, since the life of the battery is shorter than the life of the input/output unit containing the sensor or actuator, the battery must be replaced when its residual capacity has become low. When the battery is being replaced, the power supply to the wireless communication unit stops and so does the power supply to the input/output unit. Thus there is a problem that the input/output unit is unable to measure and manipulate the state quantity (i.e. it goes offline) while the battery is being replaced.
(3) Battery Cannot be Replaced while Plant is Operating
In the case of a wireless field device installed at a location where explosions must be prevented (an explosion-prevention area), the battery cannot be replaced while the plant is operating unless both the wireless field device and the battery meet explosion-prevention standards. Conceivable methods for replacing a battery when at least one of the wireless field device and the battery fails to meet explosion-prevention standards are: (a) replacing all batteries in explosion-prevention areas while the plant has stopped operating due to an inspection or the like and flammable gas is not being used, and (b) removing the wireless field device and replacing the battery in a location that is not an explosion-prevention area, and then reinstalling the wireless field device in its original location.
With the former method, the opportunity to replace the battery is limited to a time when the plant has stopped operating; in addition, a great many batteries must be replaced mechanically in a short time. Consequently, there is a problem that even batteries with sufficient residual capacity are inevitably replaced. With the latter method, since the wireless field device must be removed and then reinstalled, there is a problem that considerable time and cost is required.